1. Field of the Invention
The present invention relates generally to catheters that treat a stenosis site while simultaneously providing occlusion, and more generally to low profile catheters.
2. Description of the Related Art
Coronary heart disease is an extremely common disorder and is the leading cause of death in the U.S. Damage to, or malfunction of, the heart may be caused by narrowing or blockage of the coronary arteries (atherosclerosis) that supply blood to the heart. Myocardial infarction (i.e., dying or dead heart muscle) can result from atherosclerosis, especially from an occlusive or near occlusive thrombus that overlies or is adjacent to atherosclerotic plaque. Thrombi and emboli often result in myocardial infarction, and these clots can block the coronary arteries, or can migrate further downstream, causing additional complications. Should a blockage form at a critical place in the circulatory system, serious and permanent injury, or even death, can occur. To prevent this, some form of medical intervention is usually performed when significant blockage is detected.
Various intervention techniques have been developed to reduce or remove blockage in a blood vessel, allowing increased blood flow through the vessel. One technique for treating stenosis or occlusion of a blood vessel is balloon angioplasty. Generally, a percutaneous or arterial sheath is introduced through a puncture or incision in the patient's skin to provide percutaneous access to blood vessels. This is followed by insertion of a balloon catheter through the arterial sheath and its advancement through the blood vessels to the target site, where the occluded blood vessel is then dilated. The catheters are commonly guided through blood vessels by thin wires called guidewires, which may be either solid or hollow.
Angioplasty balloon catheters can be roughly divided into three categories: over-the-wire (OTW) systems, single-operator-exchange (SOE) or monorail systems, and fixed-wire systems (also called "balloon-on-a-wire"). In an OTW system, a solid guidewire is used to guide a balloon catheter, which is tracked coaxially over the guidewire and can be moved relative to it. SOE balloon catheters are modified OTW catheters, i.e., only the distal portion of a SOE balloon catheter tracks coaxially over the guidewire. In a fixed-wire system, tubing is in fluid communication with a balloon mounted at its distal end to supply inflation fluid to the balloon. The tubing typically has a soft tip at its distal end to guide the placement in the vessel.
It can be difficult, however, to treat plaque deposits and thrombi in the coronary arteries, since the coronary arteries are small, making it difficult to access them with commonly used catheters. Vessels as small as 3 mm in diameter are commonly found in the coronary arteries, and even the diameter of certain saphenous vein bypass graft vessels can be as small as 3 or 4 mm.
The application of balloon angioplasty to certain blood vessels has been limited by the risk of forming emboli during the procedure. For example, when angioplasty is applied to lesions in the carotid artery, there is the possibility of dislodging plaque from the lesion, which can enter the various arterial vessels of the brain and cause permanent brain damage.
Another angioplasty-related complication stems from the wide range of sizes of the emboli resulting from the procedure. Although definitive studies are not available, it is believed that emboli may have diameters anywhere from tens to a few hundred micrometers. More specifically, emboli which are considered dangerous to the patient may have diameters as large as 200 to 300 micrometers or even greater. Thus, an effective emboli containment and/or removal system must be able to accommodate relatively large embolic particles while still fitting within relatively small vessels.
These difficulties are not limited to, say, the carotid arteries. Indeed, balloon dilatation of saphenous vein grafts is more likely to produce symptomatic embolization than dilatation of the coronary arteries, not only because of the difference in the plaque, but also because vein grafts and their atheromatous plaques are generally larger than the coronary arteries to which they are anastomosed. Therefore, balloon angioplasty of vein grafts is performed with the realization that involvement by friable atherosclerosis is likely. Because of these complications and high recurrence rates, angioplasty and atherectomy are generally contraindicated for old, diffusely diseased saphenous vein grafts, thereby limiting the options available for minimally invasive treatment. However, some diffusely diseased or occluded saphenous vein grafts may be associated with acute ischemic syndromes, necessitating some form of intervention.
Yet another difficulty with angioplasty is the limited time available to perform the emboli removal procedure. That is, in order to contain the emboli produced as a result of intravascular therapy, the vessel is generally occluded, meaning that no blood perfuses through the vessel to the end organ. Thus, depending upon the end organ, the complete angioplasty procedure, including time for therapeutic treatment as well as exchanges of angioplastic balloons, stents, and the like, must generally be completed within just a few minutes.
Accordingly, there is a need for a low profile angioplasty device that provides containment of emboli and other particulates.